A contact electrode or a through-hole electrode is conventionally formed from an electrolytic copper plating film in an electrolytic plating method by use of an electrolytic copper plating solution, the method depositing and growing an electrolytic copper plating film in a via formed on a high-density mounting substrate, a semiconductor substrate, and a semiconductor package substrate.
In order to improve physical properties and deposition properties of a plating film, an additive such as an accelerator, a suppressor, and a leveler is added to the electrolytic copper plating solution described above.
As an accelerator, SPS (bis (sodiumsulfopropyl) disulfide), for example, is used.
As a suppressor, PEG (poly (ethylene glycol)), for example, is used.
As a leveler, a polyamine, for example, is used.
In order to stabilize the quality of the plating film, it is important to control and adjust amounts of additives contained in the electrolytic copper plating solution (concentrations of the accelerator, suppressor, and leveler). The additive, however, decomposes or degenerates as time elapses from a point of time when a plating reaction starts. Controlling additives therefore requires consideration of this point.
The cyclic voltammetry stripping (CVS) method is generally used to control additives. The CVS method repeatedly changes a potential of a platinum rotating disk electrode at a constant rate in a plating solution. This causes a metal plating film to be repeatedly deposited and dissolved on a surface of an electrode.
The CVS method keeps a potential scanning rate constant. Hence a dissolution peak area on a voltammogram is generally proportional to an average deposition rate, which is closely related to a concentration of an additive in the plating solution.
In the CVS method, preparing a calibration curve of a standard plating solution makes it possible to carry out quantitative analysis of an additive in a sample plating solution.
Conventional CVS devices using the CVS method pose several technical problems. For example, even if the additive in the electrolytic plating solution deteriorates due to decomposition and changes according to a period of time elapsing from the start of a plating reaction, a conventional CVS device includes the amount of deteriorated additive in the additive concentration when analyzing the sample plating solution.
The technique described in PTL 1 is known as an analysis method which considers such degradation of an additive (in other words, decomposition and changes of an additive in an electrolytic copper plating solution).
PTL 1 discloses using the CVS method to analyze MPSA (3-mercaptopropylsulfonic acid), a decomposed product of an SPS that is added as an accelerator.
PTL 2 discloses using the voltammetric method to analyze decomposition products of a leveler component.
The analysis methods disclosed in PTLs 1 and 2, however, pose a problem of requiring complicated operations, though these methods can be carried out with a conventional CVS device. More specifically, these methods require repetitive potential scanning to investigate how a potential varies or to measure two types of plating solutions prepared at different dilution ratios.
The techniques described in PTLs 3 and 4 describe simpler methods of analyzing the effect of decomposition products of additives contained in an electrolytic copper plating solution than the methods described in PTLs 1 and 2.
PTL 3 discloses an analysis method of obtaining an amount of an additive by applying constant current electrolysis to an electrolytic copper plating solution containing a brightener and a leveler as additives to yield a time-potential curve.
PTL 4 discloses an analysis method of determining a state of an electrolytic copper plating solution containing an additive from a time-potential curve yielded by application of constant current electrolysis to the electrolytic copper plating solution.
Carrying out the analysis methods of PTLs 3 and 4 involves using a rotary electrode.